Campaigners claim Barclays bank – already mired in scandal – made half a billion pounds in two years from so-called “food speculation”. The practice involves gambling on food prices in the financial markets.

Traders buy and sell “future contracts” in food, hoping to profit from the change in prices due, for instance, to a drought, natural disaster or other crisis.

These contracts have been used for hundreds of years, guaranteeing farmers a price for their crops at a future date regardless of unforeseen weather conditions.

But they can also be bought and sold by speculators who have no interest in the actual food being sold and, since the 2008 financial crisis, have been seen as an easy way to make a huge profit.

Traders working for the world’s biggest banks keep an eye on weather patterns and other factors, often delighting at the misfortune of farmers whose crops are wiped out – because it means their profits go up.

But the very fact that banks – using money from pension funds and insurance firms – are betting billions on future wholesale food prices can cause the cost of groceries to rocket.

Since 1996, the share of the markets for basic foods held by bankers has increased from 12% to a 61%, with the amount of money traded rising to £79billion today.

Barclays is the UK bank with the greatest involvement in food futures trading, along with US banking giants Goldman Sachs and Morgan Stanley.

This, and not the global recession, is what has helped push food prices to 30-year highs, causing sharp price fluctuations that have little to do with the supply of food, say campaigners.

Earlier this year Barclays Capital analysts admitted to clients that speculation on food commodities did push up prices.

Even the boss of food giant Unilever, Paul Polman, blamed cavalier traders for higher grocery bills. He said: “Food inflation has attracted speculators for short-term profit at the expense of people living a dignified life.”

In 2011 British financier Anthony Ward caused the price of cocoa beans to rocket by 20% in just three days after snapping up 240,100 tonnes in a £648million deal – pushing chocolate prices to a 22-year high.

And just in the last month the price of staple crops such as corn, wheat and soya soared by as much as 30% thanks to the greedy dealings of other speculators, according to the World Bank. The greatest impact is inevitably felt in developing countries, where the slightest rise in the cost of staples like rice and wheat can push families to the brink of starvation.

High prices for basic foodstuffs, combined with the global economic slump, have pushed 115million more people into poverty since 2008, bringing the total number of hungry people in the world to 925million.

Shop prices in the UK have risen on average by 37.9% in the past seven years, according to the Office of National Statistics. In April, average UK food prices were 4.2% higher than a year earlier.

With the average wage of low income families rising by just 22% between 1998 and 2009, it means that households cannot spend as much as they used to on food.

Meanwhile, bankers continue to cash in on the misery of others and line their own pockets.

According to the WDM, Barclays made as much as £529million from its “food speculation activities” in 2010 and 2011, while Goldman Sachs earned £600million in 2009 alone.

Christine Haigh, from the World Development Movement which released yesterday’s report, says: “The food-price spikes over the past few years have had a devastating impact on the world’s poorest people.